Tallinn Manual

The Tallinn Manual on the International Law Applicable to Cyber Warfare is not an official document, but instead an expression of opinions of a group of independent experts acting solely in their personal capacity. It does not represent the views of the NATO CCD COE, itsSponsoring Nations, or NATO. It is also not meant to reflect NATO doctrine. Nor does it reflect the position of any organization or State represented by observers.

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the use of force
acts of non-State actors, including individuals, organized groups, and
terrorist organizations, unless they are attributable to a State pursuant to
the law of State responsibility (Rule 6). In such a case, it would be the State,
not the non-State actor, which is deemed to be in violation. The actions of
non-State actors may be unlawful under international and domestic law,
but not as a violation of the prohibition on the use of force.
6. The fact that a cyber operation does not rise to the level of a use of
force does not necessarily render it lawful under international law. In
particular, a cyber operation may constitute a violation of the prohibition
on intervention. Although not expressly set out in the United Nations
Charter, the prohibition of intervention is implicit in the principle of
the sovereign equality of States laid out in Article 2(1) of the United
Nations Charter. It is mentioned in a number of treaties and United
Nations resolutions, the most signiﬁcant of which is the Declaration on
Friendly Relations. According to the International Court of Justice, the
principle is ‘part and parcel of customary international law’.4
7. The precise scope and content of the non-intervention principle
remains the subject of some debate. In the Nicaragua case, the International Court of Justice held that ‘the principle forbids all States or
groups of States to intervene directly or indirectly in the internal or
external affairs of other States’.5 Therefore, ‘a prohibited intervention
must accordingly be one bearing on matters in which each State is
permitted, by the principle of State sovereignty, to decide freely. One of
these is the choice of a political, economic, social and cultural system,
and the formulation of foreign policy.’6 For instance, the Court held
that supplying funds to insurgents was ‘undoubtedly an act of intervention in the internal affairs of Nicaragua’, although not a use of force.7
8. It is clear that not all cyber interference automatically violates the
international law prohibition on intervention; ‘interference pure and
simple is not intervention’.8 As noted by the Court in Nicaragua, ‘intervention is wrongful when it uses methods of coercion’.9 It follows
that cyber espionage and cyber exploitation operations lacking a coercive
element do not per se violate the non-intervention principle. Mere intrusion into another State’s systems does not violate the non-intervention
4
6
8
9
5
Nicaragua judgment, para. 202.
Nicaragua judgment, para. 205.
7
Nicaragua judgment, para. 205.
Nicaragua judgment, para. 228.
I Oppenheim’s International Law: Peace 432 (Robert Jennings and Arthur Watts eds.,
9th ed. 1992).
Nicaragua judgment, para. 205.